Photon router sets stage for quantum computers

London: In an effort to overcome the difficulties in building quantum computers, scientists have developed a photonic router - a quantum device based on a single atom that enables routing of single photons (particles of light).

"In a sense, the device acts as the photonic equivalent to electronic transistors, which switch electric currents in response to other electric currents," explained Barak Dayan, head of the quantum optics group at Weizmann Institute of Science in Rehovot, Israel.
At the core of the device is an atom that can switch between two states.

The state is set just by sending a single particle of light - or photon - from the right or the left via an optical fibre.

The atom, in response, then reflects or transmits the next incoming photon, accordingly.

This atom-based switch is solely operated by single photons - no additional external fields are required.

The photons are not only the units comprising the flow of information, but also the ones that control the device.
This achievement was made possible by the combination of two state-of-the-art technologies.

"One is the laser cooling and trapping of atoms. The other is the fabrication of chip-based, ultra-high quality miniature optical resonators that couple directly to the optical fibres," Dayan added.

The main motivation behind the effort to develop quantum computers is the quantum phenomenon of superposition, in which particles can exist in many states at once, potentially being able to process huge amounts of data in parallel.

"The road to building quantum computers is still very long, but the device we constructed demonstrates a simple and robust system, which should be applicable to any future architecture of such computers," Dayan emphasised in a paper that appeared in the journal Science.